Method and system for facilitating no-break power transfer

Abstract

An improved method and system for facilitating no-break power transfer between an APU and a main engine includes determining a required APU speed for conducting power transfer based on various APU operating parameters, such as engine speed, fuel, environmental temperature, etc. The APU controller then adjusts the APU speed up or down to the required APU speed. Communication between an aircraft computer and the APU controller may also be provided so that operational data can be exchanged to adjust the electrical load of the aircraft below a maximum load threshold set by the APU, avoiding overloading of the APU during power transfer. By exchanging operational data between the APU controller and the aircraft computer, both the APU and the electrical load can be adjusted to optimize no-break power transfer despite varying APU operating conditions and main engine generator frequencies.

1. A method of facilitating power transfer between a main engine and an auxiliary power unit (APU), comprising:
 obtaining a main engine generator frequency; 
 determining a target APU speed that will generate an APU generator frequency that is the same as the main engine generator frequency; 
 adjusting an actual APU speed to the target APU speed; 
 conducting the power transfer between the main engine and the APU; 
 determining an APU rate limit, wherein the step of adjusting the actual APU speed includes keeping an adjustment rate below the APU rate limit; and 
 the adjustment of said actual APU speed is taken to occur rapidly, but without extending said APU rate limit. 
 
   
   
     2. The method of  claim 1 , wherein the step of determining the target APU speed comprises checking a look-up table linking a plurality of APU frequencies with a plurality of corresponding target APU speeds. 
   
   
     3. The method of  claim 1 , wherein the APU rate limit is determined based on at least one fuel schedule. 
   
   
     4. The method of  claim 1 , wherein the step of conducting power transfer comprises connecting the main engine and the APU to a communication bus. 
   
   
     5. An engine control system that facilitates power transfer between a main engine and an auxiliary power unit, comprising:
 a control unit in communication with an aircraft load management system; 
 an APU controller in communication with the APU; 
 a communication bus that forms a communication link between the control unit and the APU controller, 
 wherein the APU controller obtains a main engine generator frequency from the control unit, determines a target APU speed that will generate an APU generator frequency that is the same as the main engine generator frequency, and adjusts an actual APU speed to the target APU speed to allow power transfer between the main engine and the APU, and the APU controller determines an APU rate limit and adjusts the actual APU speed at an adjustment rate below the APU rate limit; and 
 the adjustment of said actual APU speed is taken to occur rapidly, but without exceeding said APU rate limit. 
 
   
   
     6. The engine control system of  claim 5 , wherein the APU controller obtains the target APU speed by checking a look-up table linking a plurality of APU generator frequencies with a plurality of corresponding target APU speeds. 
   
   
     7. The engine control system of  claim 5 , wherein the APU controller determines the maximum APU load by checking a look-up table linking the target APU speed with at least one main engine operating parameter.